1. Field of the Invention
The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a metal separator in a stacking direction. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes. The metal separator includes a seal member. A passage for at least a reactant gas extends through a corner of the metal separator in the stacking direction.
2. Description of the Related Art
For example, a polymer electrolyte fuel cell employs a membrane electrode assembly (electrolyte electrode assembly) which includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a solid polymer ion exchange membrane. The membrane electrode assembly is sandwiched between separators. In use, several tens to hundreds of fuel cells are stacked together to form a fuel cell stack.
In the so called internal manifold structure, passages for reactant gases and a coolant extend through the fuel cells in the stacking direction. In the structure, reactant gas flow fields for supplying reactant gases along electrode surfaces, coolant flow fields for supplying a coolant along the separator surfaces in each of the cells, or in every certain number of cells, and the passages need to be sealed desirably.
In the metal separator of a type in which a seal member is formed integrally with a thin metal plate, in order to achieve size and weight reduction, the thickness of the metal plate is reduced. Thus, at the time of stacking the fuel cell, when displacement of the seal positions between adjacent two metal separators (hereinafter also referred to as the seal displacement) occurs, by the reaction force of the seal member itself (the moment caused by the linear pressure of the seal member), the metal plates tend to be deformed significantly. Thus, it may not be possible to maintain the sealing performance in an area where the stress tends to be concentrated, for example, at the corner of the passage.
In this regard, for example, a fuel cell as disclosed in Japanese Laid-Open Patent Publication No. 06-267567 is known. As shown in FIG. 7, packings 3 are provided on both sides of a cell 1 of the fuel cell through spacers 2. On one surface of the cell 1, a bipolar separator 4 is provided. A large number of the cells 1 and the bipolar separators 4 are stacked together to form a stack body 5. The stack body 5 is provided between flanges 7 through end separators 6. By tightening the flanges 7 together by bolts 8, a predetermined tightening force is applied to the stack body 5.
In the conventional technique, the packings 3 are provided on both sides of the cell 1 through the plates of the spacers 2. The packings 3 seal a plurality of passages 9 formed in the bipolar separators 4. In the structure, when the bipolar separator 4 is formed by a thin metal separator, if any seal displacement occurs due to variation in the size of the product or assembling accuracy, the bipolar separator 4 bends by the moment of the seal linear pressure, and the sealing performance is lowered.